Post-partum hemorrhage is a serious complication in obstetric practice. The aim of this study was to investigate, in vivo, the effects of 15 methyl-prostaglandin F2 alpha (Prostinfenem, Upjohn, Sweden) on uterine activity and hemorrhage. Twenty-seven women were included in the study and, in accordance with our clinical routine, all were given oxytocin (10 IE Syntocinon) intramuscularly immediately after delivery. In cases of heavy bleeding and signs of uterine atony, ethylergometrine (0.2 mg Methergin) and oxytocin (40 i.e. Syntocinon in 500 ml, 5.5% glucose) were administered intravenously. If this therapy failed, the woman was given an intravenous infusion of 15-methyl-prostaglandin F2 alpha (0.25 mg Prostinfenom, in 500 ml, 5.5% glucose). Myometrial activity was quantitated in 5 women by a micro-transducer introduced into the uterine cavity. The treatment resulted in a contracted uterus and cessation of bleeding within 12.5 min (mean). The intra-uterine pressure registered a prompt effect regarding both amplitude and frequency of uterine contractions.